A general optical communication module has a board and a casing that houses the board. A board included in an optical communication module is generally called a “module board” and is distinguished from a board (generally called a “host board”) included in a communication device, a transmission apparatus, etc. to which a communication module is connected. In the following description, in accordance with the above-mentioned distinction, the board included in the optical communication module may be referred to as a “module board,” and the board included in the communication device or the transmission apparatus may be referred to as a “host board” in some cases. Also, a communication device, a transmission apparatus, and the like to which a communication module is connected may be collectively referred to as a “communication device.”
A plurality of elements are mounted on the module board. For example, a light emitting element and a driving element driving the light emitting element are mounted on the module board, and a light receiving element and an amplifying element amplifying electric signals output from the light receiving element are mounted thereon. Further, a lens optically coupling the light emitting element and the light receiving element with an optical fiber is provided on the module board.
Various elements mounted on the module board emit heat during the operation, and in particular, the driving element generates a large amount of heat. In view of this, a technique has been proposed in which heat generated from an element mounted on the module board is transferred to the casing by a thermal via provided in the module board so as to be radiated from the surface of the casing (Japanese Patent Application Laid-Open Publication No. 2015-92524).
In addition, a technique has been proposed in which a board on which an electronic component is mounted and a casing that houses the board are fastened by a bolt screw to reduce a contact thermal resistance between the board and the casing (Japanese Patent Application Laid-Open Publication No. 2014-36033). To be specific, Japanese Patent Application Laid-Open Publication No. 2014-36033 discloses a way of pressing the board against the casing while applying pressure to the board by tightening a bolt screw.